CallWin32 is a
plugin for the Red Squirrel emulator (emulates an ARM-based Acorn computer)
which permits RISC-OS to make Win32 calls in the context of the emulator.
NEW: Now any Win32 code can invoke execution of up to 64 preinstalled
RISC-OS code handlers.

It also comes with a number of tools which use CallWin32 and they provide
the following:

Passes idle RISC-OS time back to Windows so CPU isn't always at 100% (NEW:
Now *configure-able in aggressiveness)

24th September 2002 v0.95: Fixed bug where mouse movement over the
RS window when RS window didn't have focus still caused RO ptr to move.
Coded up the RSTools BBC Basic program as a module task. Added wheel
movement to scroll translation. Added * commands to configure features. Made
* commands into *configure commands. Had mouse movement issue a service call
which if unclaimed then moved mouse. Fixed bug where CallWin32 crashed old
IOC machine models. Released publicly.

20th September 2002 v0.90: Graeme finally added a method of
obtaining the RS window handle, so debugged everything and turned TestMouse
into a module. Released publicly.

Downloads:

Note: CallWin32 binaries will
only work with v0.6 of Red Squirrel (or the equivalent VirtualAcorn).
You should be able to recompile them against a newer version if you wish -
note that I cannot help you do this.